As the cost of urban land increases, the use of multi-storied parking structures increases over traditional parking lots located at grade level. Parking structures generally serve office buildings, shopping centers, travel departure points and high-density dwellings.
The nature of parking structures has evolved from utilitarian "garage-like" structures to well-lit, inviting spaces that are architecturally compatible with the buildings they serve. In addition to utilizing land more efficiently, parking structures put people closer to their destinations and provide covered access when the driver becomes a pedestrian.
Typically, the interior of parking structures includes one or more driveways that serve as the means for circulating traffic within the structure. Traffic flow can be either one-way or two-way. Parking stalls are generally located on either side of the driveway and are oriented diagonally or at right angles to the driveway.
Because of the close proximity of pedestrians to vehicles, glare from the lighting is of a greater concern than on a city street. For exterior parking lots and streets, the lighting requirements are two-dimensional in nature, and the focus is on grade level lighting. In the interior of a parking structure, the lighting requirements must be considered in three dimensions. Lighting must be provided to floors, walls, ceilings, columns and directional graphics (signage) on columns and beams. Also, vehicles need to be illuminated to a height of 30 to 42 inches above the floor.
These various requirements mandate that a luminaire be capable of casting illumination to the far extent of the parking area, down the length of the driveway, at a level 30 to 42 inches above the floor, and to locations 6 feet high on columns and walls. A luminaire with this ability will be very bright because it must project light at very high angles. Yet, it must control light so that it does not blind drivers while they negotiate tight spaces and avoid pedestrians. The luminaire must also control the amount of light spill from the garage, especially in and around sensitive residential areas.
A conflict arises from the requirement that light be cast up to 6 feet above the floor because this same light would inadvertently be cast into the eyes of drivers operating within the space. The solution to this potentially dangerous paradox is to shield offending light rays from the direction of oncoming traffic while not reducing the necessary light to other areas of the space.
Another problem with luminaires that have "volumetric" distribution patterns is that the light from these units can be very bright when viewed from the exterior of the structure. This light spill is more serious in parking structures than in other buildings because the exterior walls are generally left open. The exterior walls need to be left open to promote good ventilation because of the dangerous gasses emitted by the operation of motor vehicles. This light spill not only detracts from the night time appearance of the building, but can be in violation of "light trespass" ordinances that are becoming more prevalent across the country. The solution for this problem is the same as for protecting the visibility of drivers within the structure--a shield on luminaires located near the outside walls.